Month: November 2010

Okay, so now you’ve got a great big rocket engine. What are you going to do with it? Well, fire it, of course. Make great big and noisy smoke and fire. There’s really not much that is more thrilling than an engine test…although, I guess, launches qualify (says the old engine guy reluctantly).

Engine Test at NASA Marshall Space Flight Center

But where are you going to do this? It’s not like you can do it in your garage. You’d blow away your entire neighborhood in the matter of a few seconds and the authorities tend to frown on such antics. Take a look (and listen) again at the video clip from the “What is a Rocket?” blog article to get an idea of what I’m talking about. Also, it’s not even like you can simply hire a company that specializes in testing stuff and there are many fine companies that do just that for all kinds of products big and small. No, rocket engine testing is an endeavor that requires its own dedicated facilities and infrastructure.

Over the past fifty years, NASA has developed a number of rocket engine test facilities, but by far the single largest and dedicated site is in southern Mississippi, Hancock County to be exact, today called the NASA Stennis Space Center (SSC). This facility is just about an hour from New Orleans. It is in a very secluded, woody bayou area far from any population centers. And that was the point when it was established. Given the size of the place needed to test rocket engines and rocket stages and given the noise that such testing makes, having no neighbors is basically a requirement.

Testing for the J-2X engine is currently planned in the “A-Complex” test area. That area is composed of three test stands. There are stands A1, A2, and A3 (no, it’s not an especially colorful naming scheme, I admit).

Stands A1 and A2 were designed to look like and function like the large test stand here at the NASA Marshall Space Flight Center. They were built in the 1960’s and were originally stage test facilities to accommodate testing of the S-II stage, the second stage of the Saturn V launch vehicle that took humans to the moon. The S-II stage was, of course, powered by the original J-2 rocket engine. Then in the early 1970’s, these two stands were converted into single-engine test stands to facilitate the development of the Space Shuttle Main Engine (SSME). Test stand A2 remained dedicated to SSME up until last year. Test stand A1 over the last thirty-five years was used primarily for SSME, but it was also used in the late 1990’s for the XRS-2200 linear aerospike engine development (which used a number of heritage J-2 and J-2S component designs) intended to support the X-33 vehicle.

Test Stand A2 Under Construction, Early 1960’s

S-II Stage being Hoisted into A2 in 1967 and the First SSME Test on A1 in May 1975

Test Stand A2 Today

Test stand A3 is a new facility currently being built specifically to accommodate development of the J-2X engine. It is unique in that it simulates the atmospheric pressures at high altitudes. Because the J-2X is being designed for maximum performance and for engine start at high altitudes, it is only within such a test facility as A3 that the complete configuration of the J-2X engine can be tested. The altitude simulation capability is produced by encapsulating the entire engine within a test chamber and using a system of steam ejectors to “suck down” the chamber using the Bernoulli effect familiar to students of fluid dynamics. Basically, what you have on A3 is a series of rocket engines, powered by liquid oxygen and alcohol, used to make a huge amount of high-velocity steam that creates a low-pressure environment into which the J-2X fires (itself also making a huge amount of steam). When A3 is up and running, the J-2X testing conducted there is going to be even more impressive than the usual engine tests.

Test Stand A3 Under Construction Today

The J-2X puts out approximately 300,000 pounds-force of thrust when fully configured and operating in space. As currently rigged, each of these three test stands can handle 600,000 pounds-force of thrust and, with some modifications, significantly more (the current thrust measurement systems being the limiting factor). Back when they were testing the S-II stages on A1 and A2, those stands were seeing nearly one million pounds-force of thrust with five J-2 engines firing simultaneously.

Within the last month, I had the opportunity to tour NASA SSC and see the progress of the work being done on these test stands to support the J-2X test campaign. Below are a series of photos with some accompanying commentary.

Above is a picture looking up and into the flame bucket on Stand A2. To give you an idea about dimensions, notice the person in the blue jacket and orange hardhat down on the right-hand wide. During an engine test, this entire area is deluged with water for the purposes of cooling and sound suppression. The flame bucket diverts the rocket exhaust from shooting downwards to shooting outwards and away from the stand. The long tube-like structure in the middle is a feature unique to Stand A2. It is a passive diffuser that creates simulated high-altitude conditions while the engine is running. The difference between this passive diffuser and the active diffuser on A3 is the fact that A3 can simulate higher altitudes and can do so even when the engine is not firing.

This is a shot taken near the top of stand A3. They have not yet built in the elevator so I know firsthand that the walk to the top is just about 23 flight of stairs, give or take a couple. I’ve marked stand A2 and also stand B1, which is currently used for RS-68 engine testing that supports the Delta IV launch vehicle. Stand A1 is off to the left, out of the frame of this picture. The low white building in the middle of the picture is the control room from where they conduct engine tests on A1 and A2. The control room for A3 will be in a different building.

Above is a picture of Jason Turpin (Liquid Engine Systems Branch, ER21, NASA MSFC) and Rick Ballard (Upper Stage Engine Element Systems Engineering and Integration Manager) standing on the Level 5 deck of stand A1 with the A3 construction site in the background. The water that you see behind them is part of a canal system that runs throughout the test area. On these canals they bring in barges filled with the propellants used for the testing. Back in the day, these canals were used to float in the assembled Saturn stages. This is not, however, necessary for engine testing since a single engine can be loaded onto a truck.

Overall, this tour of the facilities showed that NASA SSC is making tremendous progress in getting the test stands ready for the J-2X development test series campaign. In only a few months, we will be making smoke and fire (mostly steam!) and rumbling the acres of swampy woodlands that surround the site. I can hardly wait!

Cain Tubular Products of St. Charles, Illinois has completed fabrication of the full set of heat exchanger (HEX) coils for the J-2X development engines. These coils have been delivered to Pratt & Whitney Rocketdyne for the next step in the fabrication process that involves integration into the hot gas ducts being assembled by Arrowhead Products in Los Alamitos, California. The very first three units are already there and in work.

Below is a photo of the Cain brothers at their facility with their handiwork on display.

The HEX is a component of the engine that contributes only indirectly to engine operation. Specifically, it is used by the rocket stage to develop pressurant gases for the liquid oxygen tank.

During flight, as the engine pulls liquid oxygen from its storage tank on the stage, and as the tank drains, you need something stuffed back into the tank to replace the liquid or it will potentially collapse. Also, due to the physics of cryogenic liquids, the pumps on the engine require a certain amount of pressure at the engine inlet in order to function effectively. From the perspective of getting payload to orbit, the most efficient stuff to put into the tank to fill the volume vacated by the liquid is warm gas. But where are you going to get warm gas while the vehicle is hurtling through space? Trying to carry it in high-pressure tanks might work, but such tanks get very heavy very fast as the vehicle design gets larger. So, the better answer is this: You make warm gas while you’re flying.

Within the engine, the HEX is placed in the discharge of the engine turbines where very hot gas is allowed to flow around the coils during operation. Dense cryogenic helium is fed into the HEX inlet, it flows within the coil tubing, that tubing is surrounded on the outside by the hot gases which makes the tubing very wary, and then, at the HEX outlet, we get very warm, much-less-dense helium. That warm helium is then fed back to the stage to pressurize the liquid oxygen tank.

While there is certainly nothing patently new or exciting about heat exchangers in general — the radiator on your automobile, for example, is a heat exchanger serving a different purpose — it should be noted that due to the extreme conditions experienced within a rocket engine, and the stringent requirements placed on this particular piece of hardware, fabrication of the J-2X engine HEXs constituted its own small development effort. Cain Tubular Products did an exemplary job in deriving a unique fabrication process for this critical part and in delivering these parts in time to support the development test program.

For as long as anyone can remember here at NASA’s Marshall Space Flight Center, the collection of engineers who analyze and evaluate rocket engine test and flight data results have been called “Datadogs.” However, that time-honored moniker is a title that must be earned. It’s not automatic based upon your job assignment. It is based upon your ability to create a coherent technical narrative derived from hundreds of pieces of data spanning pre-start purge schedules, through engine start to mainstage operation, through shutdown transients and, finally, post-test inspections. With every engine firing we ask: What happened and, more importantly, why? The Datadogs provide the answers.

So, as a regular part of the J-2X Blog, I will be inviting you into the J-2X Doghouse just to ramble a bit about rockets and rocket engines in preparation for the upcoming J-2X development testing next year.

The most basic question is, of course, what is a rocket? Often, when lost in the mountain of ten thousand details of fabrication processes and assembly procedures and structural analyses and operational manuals and information of all flavors, even rocket scientists sometimes lose sight of the most basic concepts. Yet any child who has ever blown up a balloon and then let it fly across the room as it deflates has experimented in rocketry. A rocket is simply a vehicle that is self-contained and self-propelled. It takes in nothing from its external environment and it achieves motion from Newton’s principle of a reaction resulting from every action. A rocket effectively throws stuff out the back end while what remains in the rocket moves forward thereby balancing the net sum of inertia.

In technical terms, the balloon flying across the room — likely landing in your uncle’s soup thereby causing a minor family crisis — is a pressure-fed, mono-propellant rocket. The stretchy plastic of the balloon supplies the pressure and the single propellant is the breath with which the balloon was filled. The pressure from the plastic pushes the air out the back end. The air goes one way rapidly and the balloon itself goes hurtling through space in the opposite direction. Ta-da, a rocket! And now you are privy to the NASA secret that rockets, at their most basic, conceptual level, are pretty darn simple.

So, what makes a rocket engine different than a child’s balloon? Power. In order to throw thousands of pounds of a launch vehicle into the sky and accelerate it to thousands of miles per hour, you need lots and lots of power. Rather than relying on pressure to push the working fluid out the back end, a large rocket engine like J-2X uses very powerful pumps. And, rather than relying on just the velocity generated by moving the fluids, a large rocket engine taps into the chemical energy released by combustion.

For example, during every second of operation the J-2X pumps hundreds of pounds of hydrogen and oxygen into a chamber not much bigger than a large spaghetti pot. There, these fluids combust, making steam (and residual hydrogen gas) at blistering hot temperatures of thousands of degrees. That tremendous amount of energy is then directed out the back end, accelerating the hot gases down the length of the nozzle to supersonic speeds, converting thermal energy to kinetic energy all along the way.

How much steam does this make? Well, if you ever have the opportunity to see a J-2X engine test, bring an umbrella. A full duration test will make enough steam to make its own rain cloud in the sky. Below is a video of a Space Shuttle Main Engine test in stand A2 at NASA’s Stennis Space Center in Mississippi. Tests of the J-2X will look quite similar.

Thus, the tough part about rocket engines is not their basic concept. That’s simple. The tough part is building a device that can harness the power necessary to make that simple concept useful. As we go along, we’ll discuss that tough part in more detail.

I would say that it’s a pretty safe bet that a large (very large) majority of the American population is unaware that we stand on the brink of testing the first new, large, human-rated liquid rocket developed in this country since Gerald Ford was President. I might even venture to suggest that a majority of the diverse and busy population supporting NASA also don’t know that this is the case.

Back then, during the Ford administration, the new engine was called the Space Shuttle Main Engine (SSME). Its initial development at the conceptual level began in the late 1960’s. The Space Shuttle itself wouldn’t fly until 1981, nearly six years after the first attempted engine test. Today, the engine is called J-2X and this blog represents an attempt to inform those who want to follow the exciting progress of this development effort as we approach full engine testing in early 2011.

As the name suggests, the J-2X has its roots in the Apollo Program with the J-2 engine used for the second and third stages of the Saturn V rocket that first took humans to the moon. In many ways, the original J-2 was the technological predecessor of the SSME. The J-2X design is the beneficiary of over fifty years of rocket engine experience spanning the original J-2, the SSME, the experimental J-2S, and the RS-68 engine that today powers the Delta IV commercial rocket.

The J-2X is being developed by the NASA Marshall Space Flight Center in Huntsville, Alabama, the home of the propulsion systems for the Apollo Program and the Space Shuttle Program. Our contracted partner in this development is Pratt & Whitney Rocketdyne located in Los Angeles, California. Appropriately, Pratt & Whitney Rocketdyne, taking into account corporate name changes over the years, was the developer of the liquid rocket engines that powered the Apollo Program and still powers today the Space Shuttle Program. Thus, we have assembled an experienced, formidable, and knowledgeable team for J-2X.

Your humble chronicler for this journey into the exciting final stages of J-2X development is William D. Greene. I am currently the Upper Stage Engine Element Associate Manager. The Upper Stage Engine Element is the NASA office responsible for J-2X engine design and development. For the first three and a half years of this project, I was the Systems Engineering and Integration Manager for this office. I have 22 years of experience, most of which has been in support of the NASA Marshall Space Flight Center and much of which has be dedicated to liquid rocket engine analysis, development, production, and testing. I will be charting the progress of the J-2X development effort, introducing you to the extraordinary team responsible for this effort, and sharing what I know about both this activity as well as about rocket engines in general.

This is going to be fun! C’mon along for the ride! For more information about the J-2X project, see the link to the video starring some of the key people engaged in this historic effort.